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Fair Value Measurements - Narrative (Details)	9 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Period for order of valuations (at least)	18 months

X

- Definition

Number of Minimum Months for Corporation to Order Updated Valuation

+ References

No definition available.

+ Details

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Namespace Prefix:	acnb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

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- References

No definition available.

+ Details

Name:	us-gaap_FairValueDisclosuresAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration